A growing number of reference devices are finding a more wide acceptance among designers looking for accurate, reliable, relatively inexpensive and compact indicators of rotational motion. The recently developed ring gyros are being employed in a number of aircraft and missiles and have demonstrated sufficient accuracy to make them commercially attractive. An emerging family of fiber interferometers appears to have even more potential because of their increased sensitivity, reduced susceptibility to mechanical and thermal influences and their economical considerations. A particularly promising design was disclosed in a publication by V. Vali and R. W. Shorthill and entitled "Fiber Laser Gyroscopes". This idea was presented at the East Coast Conference SPIE in Reston, Virginia on Mar. 22 and 23 of 1976. Clockwise and counterclockwise beams of coherent light bidirectionally travel through a coiled single-mode fiber. The beams are recombined by suitable detectors which provide information representative of a relative rotational displacement by the device. The Vali-Shorthill approach had a number of lenses and beam splitters that had to be precisely aligned and, consequently, it was vulnerable to the temperature changes and vibrations of its surroundings.
An improvement on the concept advocated by Vali and Shorthill formed the subject matter of a pending U.S. Patent and Trademark Application Ser. No. 014,798, entitled "3 dB Single-Mode Optical Fiber Interferometer Beam Splitter Coupler" by Matthew N. McLandrich. The inventor sought to reduce the number of components susceptible to ambient influences. His integral, unitized, continuous interferometer reduced the problems associated with a number of dissimilar elements joined together. However, as with all endeavors, it was noted that even further improved performance might be provided for by phase shifting between the counterrotating beams of light.
Phase shifting between counterrotating beams in an inertial reference device was anticipated by Jack B. Speller in his U.S. Pat. No. 3,395,270 entitled "Relativistic Inertial Reference Device". Kerr cells are included interposed in the light beam path to shift the relative phase between the countercirculating beams and hope to provide a more responsive readout. Inclusion of the Kerr cells along with the associated beam splitters, lenses and physically separated quartz loop collectively may create more drawbacks than optimistically could be compensated by the Kerr cells. The many breaks in the optical path between the source of light and the sensors all erode this type of a referencing device's ability to function properly.
Thus there is a continuing need of the state-of-the-art for an improvement to the single-mode fiber interferometer gyro which enhances the performance of the integral fiber interferometer by providing for phase biasing of its counterrotating beams yet does not compromise its inherent capabilities including being a unitized continuous device for assuring responsive indications of rotational motion.